The present invention relates to a load-synchronous Doppler charge pump with an integrated series-path regulator, and in particular, to a circuit for voltage raising for pulsed-operated loads.
A circuit is known, for example, from EP-A-0561257, and is illustrated in FIG. 4. Circuits for voltage raising are required, for example, for TDMA mobile radios, in which there are a number of time channels in one frequency band. Timeslots are used for transmission, as a result of which a relatively high battery current flows during the short transmission bursts, and leads to voltage drops in the battery and supply lines which are so high that the critical supply voltage for the integrated circuits or voltage regulators can be undershot, particularly at the end of the battery discharge time.
In the circuit illustrated in FIG. 4 for voltage raising, a battery voltage UB of, for example, 6 volts is provided. Voltage is possible via a switch S with two changeover contacts, and provides the supply voltage for the transmission output stage of a mobile radio, and the critical supply voltage for integrated circuits. To prevent the last-mentioned supply voltage for the voltage-critical circuit parts from falling below a critical value, a voltage raiser is arranged in this path. This voltage raiser contains a capacitor C and a charging resistor R index L. The capacitor is charged when no transmissions are being made. During the transmission bursts which are transmitted in the transmission output stage, the voltage of the capacitor C in the supply path to the voltage-critical circuit parts is added to the battery voltage. The voltage raiser is followed by a regulator for, for example, 5 volts, whose output voltage is supplied to the downstream circuit parts for control purposes. The switched voltage raiser as shown in FIG. 4 ensures that the input voltage to the 5-volt voltage regulator for control purposes always remains above 5 volts, even when the battery voltage UB falls well below 5 volts due to the internal resistance of the battery.
The circuit in FIG. 4 can thus be represented, in simplified form, as in FIG. 3. That is, it may be represented as a combination of a charge pump 5 followed by a linear regulator 7. The output voltage is compared with a nominal value in the linear regulator 7. Such a linear regulator 7, which follows the charge pump 5, can thus stabilize the output voltage.
In one embodiment of the invention, there is a circuit for voltage raising for pulsed-operated loads. The circuit includes, for example, a capacitor, a switching unit with a controllable transistor, and a control circuit, wherein the capacitor is driven by the switching unit such that it is charged by a battery during the time in which the load is not in operation, and a voltage is added to the voltage from the battery during operation of the load, the output voltage of the circuit is regulated by the control circuit during operation of the load for voltage raising such that it corresponds to a nominal value, and the control circuit varies the resistance of the transistor in order to regulate the output voltage.
In another aspect of the invention, the transistor is connected in parallel with the capacitor.
In another aspect of the invention, the switching unit also has a make-contact switch connected in series with the transistor.
In yet another aspect of the invention, when the load is not in operation, the transistor is switched off.
In another aspect of the invention, the transistor and the control circuit are part of an integrated circuit.
In another embodiment of the invention, there is a mobile radio. The mobile radio includes, for example, a circuit for voltage raising including a capacitor, a switching unit with a controllable transistor, and a control circuit, wherein the capacitor is driven by the switching unit such that it is charged by a battery during the time in which the load is not in operation, and a voltage is added to the voltage from the battery during operation of the load, the output voltage of the circuit is regulated by the control circuit during operation of the load for voltage raising such that it corresponds to a nominal value, and the control circuit varies the resistance of the transistor in order to regulate the output voltage.